MIMO Volterra polynomial equalizer for PDM ultrahigh-order QAM signals

Area of Science:

• Optical Communications
• Signal Processing

Background:

• Coherent optical transmission systems face nonlinear distortions.
• Polarization-division multiplexing (PDM) and high-order modulation like 4096-QAM increase data rates but exacerbate nonlinearities.
• Existing equalizers like single-input single-output Volterra nonlinear equalizers (SISO VNLEs) have limitations in mitigating these distortions.

Purpose of the Study:

• To propose and experimentally demonstrate a multiple-input multiple-output Volterra polynomial equalizer (MVPE).
• To evaluate the performance of the MVPE in a probabilistic shaping (PS) PDM 4096-QAM system.
• To compare the MVPE's effectiveness against conventional SISO VNLEs.

Main Methods:

• Implementation of an MVPE for simultaneous equalization of in-phase (I) and quadrature (Q) components across both X and Y polarizations.
• Experimental setup of a PS-PDM-4096-QAM coherent optical transmission system.
• Performance evaluation using normalized generalized mutual information (NGMI) and receiver sensitivity measurements.

Main Results:

• The MVPE effectively alleviates nonlinear distortions in the PS-PDM-4096-QAM system.
• The NGMI reached the threshold of DVB-S2 low-density parity-check (LDPC) codes with 20% overhead.
• A receiver sensitivity improvement of approximately 2.8 dB was achieved compared to SISO VNLEs.
• The MVPE maintained nearly similar computational complexity to SISO VNLEs.

Conclusions:

• The proposed MVPE is a highly effective solution for mitigating nonlinear distortions in advanced coherent optical systems.
• MVPE offers significant performance gains in receiver sensitivity without a substantial increase in computational complexity.
• This technology advances the feasibility of high-capacity optical transmission using PS-PDM-4096-QAM.